Low drop-out (LDO) voltage regulators are linear voltage regulators that operate with a small power supply to output voltage drop. LDO regulators provide a DC output voltage via a pass transistor situated between the power supply and the output. The drop-out voltage is related to output current via the on resistance of the pass transistor. Typically, the pass transistor is a PMOS transistor that does not require its gate voltage to be driven high and the drop-out voltage is limited by the on resistance of the PMOS transistor. Alternative strategies include gate voltage pumping, which is often dismissed due to noise, power consumption and startup time constraints.
LDO regulators can be used in automotive applications, where external power supply voltages fluctuate and only small voltage drops are permitted between the external power supply voltages and the output voltages of the LDO regulator. However, the automotive environment is a noisy environment and power supply ripple is sometimes transferred to the output of the LDO regulator. Using external capacitors to reduce ripple increases costs and reduces reliability.
Some LDO regulators are coupled to digital circuitry that generates current spikes, such as switching current spikes and current spikes due to pre-loading and un-loading of capacitances. Regulators with fast load regulation respond to the current spikes, but produce electro-magnetic interference (EMI) via the power supply lines. This EMI is a problem in some situations, such as in sensors using a current interface, mobile phones, and integrated circuits in automotive applications. For these and other reasons, there is a need for the present invention.